(1) Field of the Invention
The present invention relates to substrate processing methods for fabrication of semiconductor integrated circuits or other purposes, and more particularly relates to substrate processing methods for processing substrates, e.g., implanting ions into substrates or cleaning substrates, while moving substrates at high speed.
(2) Description of Related Art
With a higher degree of integration of semiconductor integrated circuit devices, the sizes of gate electrodes of metal oxide semiconductor (MOS) transistors are becoming finer and finer. This reduces the physical strengths of gate electrodes, and thus gate electrodes have come to easily suffer damage due to shock.
In the case where source/drain regions of MOS transistors are formed by ion implantation, a higher degree of uniformity is demanded for the impurity profile over the wafer plane with a higher degree of integration. Furthermore, gate dielectrics reduced in thickness to approximately several nanometers due to scaling have been extremely likely to produce a dielectric breakdown due to charge-up caused by the implantation of ions into gate electrodes or implantation of ions into substrates using gate electrodes as masks.
Conventionally, in general, an impurity is introduced into a wafer by scanning the top surface of the wafer with ion beams having a narrowed diameter. The reasons for this are as follows: first, the uniformity of the impurity profile and the impurity concentration over the wafer plane is enhanced in high-current ion implantation, in particular, ion implantation for the formation of source/drain regions; and furthermore continuous application of beams to the wafer at a high ionic concentration is restrained from producing a dielectric breakdown due to charge-up and thus causing damage.
To be specific, methods for uniformly introducing an impurity into the entire surface of a wafer with ion beams having a narrow diameter include a method in which a semiconductor substrate is allowed to travel at high speed in the vertical direction to fixed incident ion beams without scanning the wafer plane with ion beams. This method is disclosed in, for example, Japanese Unexamined Patent Publication No. 5-135731.
FIG. 4A illustrates an end station part of a batch-type ion implantation apparatus using the above-mentioned method. Semiconductor substrates are placed on the end station part. As illustrated in FIG. 4A, a plurality of semiconductor substrates 11 are placed and fixed on a large-diameter disk 10, and the disk 10 can rotate about a rotational shaft 12. Such an end station part and other components are placed as a whole under a high vacuum atmosphere.
FIG. 4B illustrates the state of the end station part during ion implantation when obliquely viewed. During ion implantation, the disk 10 usually rotates at a high speed of 1000 rpm (revolutions per minute) or more. Simultaneously, the disk 10 itself linearly moves up and down. While the disk 10 is moving as described above, ion beams 13 are applied to the disk 10.
In the above-mentioned manner, the top surfaces of the semiconductor substrates 11 are uniformly scanned with the ion beams 13. As a result, an impurity is introduced generally uniformly into the semiconductor substrates 11.